Pyrotechnic smoke compositions, based on phosphorus, phosphorus-containing compositions, or HC smoke compositions, used in mortar smoke bodies, generate a fog consisting of finely divide acid droplets or hydroscopic salts, such as zinc chloride, (West German Patent Specification No. 1,185,510, West German Patent Specification No. 1,196,548 and West German Patent Specification No. 1,300,454). Furthermore, it is known to generate fog-clouds by the discharge of strongly hygroscopic acids such as chlorosulphonic acid, or of acid chlorides, such as phosphorus pentachloride or of liquids such as titanium tetrachloride, or of mixtures of the above-mentioned acids, acid chlorides or liquids in combination with amines, such as, for example, triethylamine as disclosed in the West German Unexamined Patent Application (Offenlegunqeschrift) No. 2,232,763. Furthermore, it is known to generate fog-clouds with fine droplets by dispersing oil or oil/water emulsions by means of compressed gas generators.
While fire risk, risk of poisoning by the usually toxic fog, and only low scattering and absorption in the near infra-red range are generally inherent in pyrotechnic fogs, the acid fogs, acid chloride fogs, liquid fogs and two-component fogs, produced from the latter types with amines, possess, apart from only low scattering and absorption in the near infra-red range, the disadvantage of acute chemical attack, corrosion and toxicity. In addition, the oil fogs or oil/water emulsion fogs are completely permeable to the wave length range of the near infra-red light, (0.8 to 14 m). Moreover, it is known from the British Patent Specification 638,060 to produce a stream of solid particles in the form of smoke for coating and finishing purposes.
U.S. Pat. No. 4,210,555 discloses a method for producing smoke for military purposes which allegedly produces smoke which is cold, neutral, non-toxic as well as impermeable to infra-red instruments and other instruments used in military night vision techniques. The smoke is produced by using microfine powder, having a particle diameter of from 3 to 60 .mu.m, being impenetrable to visible light and infra-red light of up to 14 .mu.m wave length, and having a settling velocity of up to 5 cm/sec., which is dispersed in a very short time from a container by means of a propellant gas or explosive. Powders that can be used in practicing the invention of U.S. Pat. No. 4,210,555 are talc, kaolin, ammonium sulfate, ammonium phosphates, calcium carbonates, magnesium carbonates, sodium hydrogen carbonate, and other free-flowing powders, or powders that have been rendered flowable, which can form buoyant clouds upon being dispersed as by discharge of a compressed gas.
By the use of the above-mentioned neutral, cold and nontoxic powders, the disadvantages of toxicity and of fire risk are excluded, as the powder is finely atomized in the cold. It is alleged that the essential advantage, however, is that military night vision techniques, particularly the use of temperature entropy recording instruments, are unable to penetrate the artificial dust cloud and thus are unable to record a temperature entropy diagram of the terrain behind the cloud. Dispersion of the powder can be effected by known methods by means of propellant gas, e.g. CO.sub.2, N.sub.2 or compressed air, inside or outside the receptacle containing the powder. Similarly, it is also possible to apply as the propellant a gas refrigerant gas or a propellant gas from gas generators. Release or liberation of the compressed gas onto the powder in the container is preferably effected electrically, e.g. by operating a pyrotechnic power element or an electrical-mechanical element.
Ejection of the powder is effected through an atomizerlike device having an ascending tube in the interior of the powder container, such tube ending in a suitable nozzle aperture for the fine division or dispersion of the powder into the surrounding atmosphere. In accordance with the usual technique, separation between the release of compressed gas onto the powder and the efflux of the powder through the nozzle can be accomplished, for example, by means of an additional valve and/or a bursting-disc on the container. In this way, rapid and safe discharge of the fog-cloud is possible.
U.S. Pat. No. 4,406,815 discloses an aerosol which allegedly reduces optical transmission by an attenuation technique which utilizes an aerosol of finely divided particles e.g. activated carbon black. The carbon black has a considerable "micro porosity," that is a small scale porosity with holes having a size less than the optical wave lengths (i.e. &lt;0.1 .mu.m). Furthermore the carbon black particles have a very irregular configuration and an absorbing surface of up to 1200 m.sup.2 /g. Eighty percent of the particles have diameters which are approximately equally distributed in the range between 1 to 9 .mu.m.
U.S. Pat. No. 4,538,151 discloses electro-magnetic wave absorbing material which comprises, inter alia, a mixture of ferrite and a high molecular weight synthetic resin, carbon black and short fibers of metal. The metal fibers preferably have a length (L) of 0.1-50 mm and a length (L) to diameter (D) ratio (L/D) of larger than 10. The quantity of metal fiber is larger than 3% by weight. The metal is a high conductivity metal such as Au, Ag, Cu, Cr, Zn, Ni, Fe or alloys thereof. The ferrite may be substituted by a ferromagnetic material such as iron, cobalt or nickel. The synthetic material can comprise the titanates of lead, barium and strontium as well as lead neobate and lead zirconate.
U.S. Pat. No. 3,773,684 discloses a dipolar electrooptic composition and its method of preparation. Particles which have a dipole moment or exhibit a dipole moment in a magnetic field are suspended in a fluid medium. Illustrative of the dipole particles are herapathite particles and metals. The invention is directed primarily toward reversible effects produced by changing current polarity on fluids having suspended therein particles having a dipole moment.
It is know that smoke useful for camouflage purposes can be prepared by suspending material in a fluid medium, and vaporizing the medium using a heat source while mixing the fluid with an inert carrier gas. Both the suspended particles and the fluid carrier medium which becomes an aerosol, contribute to the "smoke". It is also known to form smoke with suspended particles by decomposing a liquid feedstock to form the particles. Proper selection of the particles, from which radar, infra-red or other electromagnetic waves are absorbed or scattered, results in a smoke opaque to both visible light and other electromagnetic radiation. The disadvantage of the prior art method is that there is a requirement for a large volume source of inert gas. Additionally, a heat source is required to produce steam which is utilized to vaporize the fluid carrier medium in a heat exchanger. An important aspect of the prior art generation process is the use of a magnetic field which aligns the particles of the feed and causes "growth" of the particles to a size to result in optimum obscurant effect of the smoke in the electromagnetic wave range of interest. The smoke produced must be essentially near ambient temperature so that it will not rise as a result of thermal convection.